/*混合的匹配模式*/
.triangle(@_,@w,@c){
    width: 0px;
    height: 0;
    overflow: hidden;
}
.triangle(L,@w,@c){
    border-width: @w;
    border-style: dashed solid dashed dashed;
    border-color: transparent @c transparent transparent;
}
.triangle(R,@w,@c){
    border-width: @w;
    border-style: dashed  dashed dashed solid;
    border-color: transparent  transparent transparent @c;
}
.triangle(T,@w,@c){
    border-width: @w;
    border-style: dashed  dashed solid dashed;
    border-color: transparent transparent @c transparent;
}
.triangle(B,@w,@c){
    border-width: @w;
    border-style: solid dashed  dashed dashed;
    border-color:  @c transparent transparent transparent;
}